Question

`NH_(4)ClO_(4)` crystallises in orthohombic structure with unit cell volume of `395 Å^(3)` . The structure of `HClO_(4).H_(2)O` will be
A. tetragonal will unit cell volume of `210 Å^(3)`
B. cubic with unit cell volume of `78Å^(3)`
C. orthorhomibic with unit cell volume of `370 Å^(3)`
D. the data given is not sufficient to find the structure.

Answer 1

Correct Answer - C
Both substances are ionic with lattice sites occupied by ions. In `HClO_(4).H_(2)O` cation is `H_(3)O^(+)` and there are no `H_(2)O` molecules of hydration. The anions in both are same i.e., `ClO_(4)^(-)` ions. `H_(3)O^(+)` and `NH_(4)^(+)` are nearly isoelectronic ( have nearly same number of electrons ) and as such occupy nearly equal space.